test: make unsafe test coercion explicit

Move test coercion out of a hidden global and require each test to import the helper so review tools and runtime scripts can see the unsafe boundary.

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

src/hooks/atlas/idle-event.test.ts

@@ -8,6 +8,7 @@ import { createBoulderState, readBoulderState, writeBoulderState } from "../../f
 import { _resetForTesting, registerAgentName } from "../../features/claude-code-session-state"
 import { handleAtlasSessionIdle } from "./idle-event"
 import type { SessionState } from "./types"
+import { unsafeTestValue } from "../../../test-support/unsafe-test-value"
 
 describe("handleAtlasSessionIdle completion nudge", () => {
   const SESSION_ID = "session-main-1"
@@ -76,7 +77,7 @@ describe("handleAtlasSessionIdle completion nudge", () => {
       return { data: {} }
     })
 
-    const ctx = testCoerce<PluginInput>({
+    const ctx = unsafeTestValue<PluginInput>({
       directory: testDirectory,
       client: {
         session: {